Space Systems Design Studio

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Flux-Pinned Spacecraft Research

Description of Flux Pinning

The flux pinning effect creates effective stiffness and damping for small motions in multiple degrees of freedom. Other researchers have focused mainly on the vertical and lateral stiffness of a connection as applied to levitation systems. The additional stiffness and damping associated with the relative attitude of the components, however, represents a valuable augmentation to the general rigid body motion of vehicles in orbit. By pinning a magnetic field in various relative positions and orientations to a HTSC and observing the system's response to an input, we can estimate the linearized properties at these specific points in configuration space. Fitting an appropriate curve to this data provides an experimentally based description of flux pinning, which informs design choices when creating a flux-pinned formation.

One potentially useful property of flux pinning occurs when the magnetic field is rotationally symmetric. As rotations about the magnetic field's axis of symmetry do not result in a change in magnetic flux passing through the HTSC surface, there is no resulting flux-pinned reaction force or torque. This unconstrained rotational degree of freedom forms the basis for creating a system of non-contacting mechanisms.

For more information, see:

• Shoer, "Flux-Pinned Interfaces for the Assembly, Manipulation, and Reconfiguration of Modular Space Systems"
• Shoer and Peck, "A Flux-Pinned Magnet-Superconductor Pair for Close-Proximity Station Keeping and Self-Assembly of Spacecraft"

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Multibody Dynamics and Control

For small motions, flux pinning can be viewed as a spring and damper acting in more than one degree of freedom. This approximation becomes less accurate as the relative position displacements increase, but it provides the foundation of a convenient linear model of the system's dynamics. In turn, this linearization allows for us to apply standard linear system analysis techniques to describe a given system's properties such as stability, controllability, and observability.

The difference in gravitational attraction between the individual bodies in a multibody space system can shift the relative positions of a static formation away from the desired states if that system does not benefit from appropriate control input or stabilizing dynamics. The additional dynamics due to flux pinning connections between rigid bodies tend to passively stabilize the relative motions of the bodies by stiffening and damping particular modes. Since the stiffness and damping associated with each degree of freedom tend to increase exponentially as the separation distance closes, flux pinning in a multibody space formation sees the most benefit in close proximity formation flight. Typical examples of this type of formation are seen in docking, object manipulation, and in-orbit assembly tasks.

For more information, see:

• Norman, "Stationkeeping and Reconfiguration of a Flux-Pinned Satellite Network"
• Norman and Peck, "Modeling and Properties of a Flux-Pinned Network of Satellites"

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Complex Structure Assembly

In addition to examining the linearized dynamics properties of a flux-pinned system, we are interested in applying this type of connection to particular vehicle formations. In these situations, the actual algorithm for assembly and reconfiguration become important. One particular formation of interest is the concept of a large aperture flux-pinned space telescope. Flux pinning represents an attractive solution to management of the relative motion of the spacecraft by offering a non-contacting, modular, reconfigurable, and passively stable connection.

For more information, see:

• Gersh, "Architecting the Very-Large-Aperture Flux-Pinned Space Telescope: A Scalable, Modular Optical Array with High Agility and Passively Stable Orbital Dynamics"
• Norman, "Stationkeeping and Reconfiguration of a Flux-Pinned Satellite Network"

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